1. Technical Field of the Invention
The present invention relates to internal combustion engines, for powering vehicles such as cars or motorcycles. More particularly, the present invention relates to an internal combustion engine incorporating a splash-resistant oil storage structure.
2. Background Art
Internal combustion engines are in wide use for powering many types of vehicles. One example of a known oil storage structure in the lower end of a crankcase, for example, includes an oil storage chamber, an oil supply pipe which extends into the oil storage chamber from above, and a pickup port provided at the lower end of the oil supply pipe. The pickup port opens near the bottom surface of the oil storage chamber (bottom surface of the crankcase). The upper end of the oil supply pipe is connected to an oil pump via an oil channel formed on a side wall of the crankcase. Oil from the oil storage chamber is drawn into the pickup port by operation of the oil pump, and supplied to respective lubricating points and cooling points of an engine.
In the oil storage structure as described above, the surface of the oil stored in the oil storage chamber tends to flow in a direction opposite vehicle movement and deviates rearwardly or forwardly in response to normal acceleration or deceleration. In addition, when the vehicle is suddenly accelerated or decelerated, the amount of deviation of the surface of the oil stored in the oil storage chamber increases, and hence the pickup port may become exposed to air and uncovered with oil.
Therefore, as disclosed in Japanese published patent document JP-A-1-141400 for example, an oil storage structure for an engine has been proposed, in which front and rear secondary oil chambers are formed respectively on the front side and the rear side of the engine. These secondary oil chambers are partitioned from the oil storage chamber by partitioning walls, and covered on top by a ceiling wall. In the oil storage structure disclosed in the reference, oil flow orifices are formed at the lower ends of the respective partitioning walls, and the respective ceiling walls are formed with air holes therein. In this arrangement, fluctuation of the oil surface in the fore-and-aft direction in case of sudden acceleration and deceleration of the vehicle can be restrained.
However, in the oil storage structure as described above, since the secondary oil chambers defined by the partitioning walls are provided only at the front and rear of the engine, fluctuation of the oil surface in the lateral direction in case of sudden turning of the vehicle cannot be restrained. Therefore, it is still possible for the oil pickup port to be temporarily uncovered during a sudden and sharp turn of the vehicle.